Quadrajet Hesitation When Accelerating

[jbwolfe]

Originally Posted by 68gmsee

I think you're gonna have to try what these guys are telling you otherwise it ain't gonna get fixed. Most of us speak from many, many years of experience.

First, I would look for another vacuum port if that one didn't fit or get some sort of adapter from local auto parts.

Next, I would tie the choke open regardless of what the vacuum does. It's still trying to close when the vacuum is low as when accelerating.

Re. vacuum testing: Go to Sears or the local auto parts store and pick up a vacuum gauge. It's something you need to have to work on these old trucks. One of the cheaper tools to own.

Re. checking for leaks: Yes, you can use the starter fluid carefully to see if the engine revs up higher when there's a vacuum leak. I prefer a 2-3 foot section of garden hose and place one end on the areas I suspect are leaking to listen for hissing sounds. Either way works.

Thank for your input. I'm going to order the book that was mentioned earlier to learn more about the Q-jets.

I'll tie the choke open and try that, I hadn't realized the vacuum would be lower when the throttle is open, makes sense.

Next time I'm in town I'm going to get a vac tester. I'll test the fuel pressure and vacuum. I will also test for vacuum leaks around the carb.

Originally Posted by jd7

Put a new holley on it and be done. That intake is way to much for that carb set up. A decent builder would have at least done a better job of cleaning the body.It looks to be a few carbs cannibalized.

I might if I had the money. I guess I wasn't very clear in the original post. The carb currently on the truck IS NOT REBUILT. That was the previous Q-jet, which had even more problems.

[BHyatt]

It would seem reasonable to me that a simple solution would be a return to the original carb and intake which you said ran fine. Problem solved.

[flyingtim01]

Just what 68 said. The vacuum gauge will get your mixture right on without having to rely on your ear.

I'd grab the carb with the electric choke. It's what I have on mine, and in my estimation, its just a simpler setup. No linkage to bend/adjust, don't have to worry about the choke stove getting gummed up when your inner intake bolts start to seep oil, and they're easier to adjust when the weather changes. Just loosen the screws holding it on and rotate. Just need to run a key on 12V wire. And if you want to be really trick, there was a member who remarked that he wired his choke in through his oil pressure wire, so it only got 12V when the engine was running, not just when the key was on (so you don't have to remember to make sure your key is in the OFF position when you don't want the choke to heat up).

BHyatt, the original setup that worked well was a 2 barrel, which for obvious reasons isn't acceptable...

[jbwolfe]

Originally Posted by 68gmsee

Put the vacuum tester in a vacuum port. The bottom manifold vacuum that I mentioned would be a good source. Any other manifold vacuum will work except for the ported vacuum that you have the advance on.

Next, adjust the idle screws as mentioned above by flyingtim but look for the highest vacuum on each one.

I just picked up a vac tester today, and a flair nut wrench set so I don't strip the bolt when I take the fuel line off next time. How do you tell which is ported vacuum and which isn't? You're talking about adjusting the two mixture screws in front right?

Originally Posted by BHyatt

It would seem reasonable to me that a simple solution would be a return to the original carb and intake which you said ran fine. Problem solved.

Aside from really wanting a 4bbl setup, the 2bbl setup had other problems of it's own.

Originally Posted by flyingtim01

Just what 68 said. The vacuum gauge will get your mixture right on without having to rely on your ear.

I'd grab the carb with the electric choke. It's what I have on mine, and in my estimation, its just a simpler setup. No linkage to bend/adjust, don't have to worry about the choke stove getting gummed up when your inner intake bolts start to seep oil, and they're easier to adjust when the weather changes. Just loosen the screws holding it on and rotate. Just need to run a key on 12V wire. And if you want to be really trick, there was a member who remarked that he wired his choke in through his oil pressure wire, so it only got 12V when the engine was running, not just when the key was on (so you don't have to remember to make sure your key is in the OFF position when you don't want the choke to heat up).

BHyatt, the original setup that worked well was a 2 barrel, which for obvious reasons isn't acceptable...

Yes I'm planning on putting the rebuilt Qjet with the electric choke on. I've already got the wire set up for the choke. In the mean time before I get the new carb, I am going to do some more tests on this carb because I'm curious about what's causing this problem. That and it wouldn't hurt to test my fuel pressure anyway.

I agree about the 2bbl being unacceptable.

[c10monkey]

I personally would swap the intake out. Looks like you have a single plane intake which is great for racing and higher rpms. But a dual plane intake is better at lower rpms and better for street use. I have a Qjet on an Eldelbrook dual plane intake and have no issues.

My 2 cents :-)

[jbwolfe]

Originally Posted by c10monkey

I personally would swap the intake out. Looks like you have a single plane intake which is great for racing and higher rpms. But a dual plane intake is better at lower rpms and better for street use. I have a Qjet on an Eldelbrook dual plane intake and have no issues.

My 2 cents :-)

How do you tell if it is a dual plane intake? I'm not really sure what that means...

Just for an update: I haven't been able to get that other used carb I was hoping for yet, and in the mean time I had to take the second used carb back to the mechanic who sold it to me for my money back, so I didn't get to mess with it anymore.

For now, I'm going to put the first Q-Jet back on, just so I can drive the truck. Hopefully I will get a different carb to try soon. If not, I'm considering buying a used Q-Jet and rebuilding it after ordering a good book.

[72CampSpecial]

Recently rebuilt/tuned my '75 Cali emissions carb..

-Cliff Rugles Book.. a must
-Cliff Rugles forum for Questions.. a must
-No one has mentioned adjusting the APT (or i missed it).. mine was way off after the re-build (this one requires a very easy carb modification, but worth it)
-Other things to consider.. Timing, Adjusting the Idle mixture screws, adjusting your idle and the APT made all the difference for me..

My truck was sluggish and ran like crap until i started dialing all those in..after many, many adjustments its running great now.

[capev86]

I personally would swap the intake out. Looks like you have a single plane intake which is great for racing and higher rpms. But a dual plane intake is better at lower rpms and better for street use. I have a Qjet on an Eldelbrook dual plane intake and have no issues.

that is not the kind of intake i would want to see on a truck, unless it is a stripped down, drag race only vehicle with a big bad engine tuned specifically for high rpm operation.

i did a similar swap on my 72 Suburban C20. i didn't care for the faulty 2bbl on the original 307, so i pulled it in favor of a Q-jet swap. i found a good deal locally on an a still in the box Edelbrock performer manifold that is designed to fit up to both square bore and spread bore carbs. this manifold is a low profile, dual plane unit that augments power in the idle-5500rpm range. it perfectly compliments the low end throttle response and top end punch the Q-jet is famous for on the street.

at the same time i swapped the rear gears from 4.57 to 4.10. the truck is soooo much more responsive and fuel economy has gone from 10/11 to 14/15. 2 out of the last 3 tank fulls have averaged 16mpg...and that is without overdrive! oh...and during idle the vacuum is over 20....according to my in dash reproduction vac gauge.

[jbwolfe]

Originally Posted by 72CampSpecial

Recently rebuilt/tuned my '75 Cali emissions carb..

-Cliff Rugles Book.. a must
-Cliff Rugles forum for Questions.. a must
-No one has mentioned adjusting the APT (or i missed it).. mine was way off after the re-build (this one requires a very easy carb modification, but worth it)
-Other things to consider.. Timing, Adjusting the Idle mixture screws, adjusting your idle and the APT made all the difference for me..

My truck was sluggish and ran like crap until i started dialing all those in..after many, many adjustments its running great now.

I'll check out that forum. What is the APT? I'd image all that is covered in the book...

Originally Posted by capev86

that is not the kind of intake i would want to see on a truck, unless it is a stripped down, drag race only vehicle with a big bad engine tuned specifically for high rpm operation.

i did a similar swap on my 72 Suburban C20. i didn't care for the faulty 2bbl on the original 307, so i pulled it in favor of a Q-jet swap. i found a good deal locally on an a still in the box Edelbrock performer manifold that is designed to fit up to both square bore and spread bore carbs. this manifold is a low profile, dual plane unit that augments power in the idle-5500rpm range. it perfectly compliments the low end throttle response and top end punch the Q-jet is famous for on the street.

at the same time i swapped the rear gears from 4.57 to 4.10. the truck is soooo much more responsive and fuel economy has gone from 10/11 to 14/15. 2 out of the last 3 tank fulls have averaged 16mpg...and that is without overdrive! oh...and during idle the vacuum is over 20....according to my in dash reproduction vac gauge.

Not to worry, the intake I put on the 350 is a DUAL plane Edelbrock Performer RPM Air Gap, and it is also designed for the idle-5500RPM range.

Sounds like your swap turned out great! Hope I can get close to those results with mine. I'd just be thrilled out of my mind if it ran well.

[luvbowties]

Originally Posted by jbwolfe

I'll check out that forum. What is the APT? I'd image all that is covered in the book...



Not to worry, the intake I put on the 350 is a DUAL plane Edelbrock Performer RPM Air Gap, and it is also designed for the idle-5500RPM range.

Sounds like your swap turned out great! Hope I can get close to those results with mine. I'd just be thrilled out of my mind if it ran well.

JB, I don't think anybody mentioned this: try adjusting timing with vac advance attached. Also, ensure vac adv is hooked to a port that is pulling vacuum even with engine idling. (If worse, u can always make changes.), but in my experience, these 2 things have worked better for me when using hei and q'jet.
Sam

[luvbowties]

*change to above: should read "with vacuum advance Un-attached and plugged, of course"...

[Haakon]

I have the same exact issue that your having! Did you ever get to the bottom of your bogging?

[geezer#99]

You got that backward snipes!
Looser tension on the secondary air valve causes the bog.
As per the apt here's a link to explain it. Yours is likely in the baseplate JB.
http://www.crankshaftcoalition.com/w...#Trouble_spots

[geezer#99]

You know Haakon you're likely better to start your own thread with your own pics and symptoms.

[Haakon]

Originally Posted by geezer#99

You know Haakon you're likely better to start your own thread with your own pics and symptoms.

No worries! I just unboxed a fresh rebuilt quadrajet from US Carbs, so hopefully I won't have to start a new thread! Thanks much!

[geezer#99]

Looking forward to your new thread Haakon about 'I just bought this rebuilt carb and can't get it to run'!!
Just sayin'!!!

[Haakon]

Originally Posted by geezer#99

Looking forward to your new thread Haakon about 'I just bought this rebuilt carb and can't get it to run'!!
Just sayin'!!!

Sorry to burst your bubble geezer.... Like night and day! If I didn't know better, I would have thought this was 1971 and I was test driving a brand new c10!!! Great job U.S.Carbs!!

[Fitz]

Originally Posted by geezer#99

Looking forward to your new thread Haakon about 'I just bought this rebuilt carb and can't get it to run'!!
Just sayin'!!!

Shoulda bought a Holley, Haakon!

[Haakon]

Originally Posted by Fitz

Shoulda bought a Holley, Haakon!

I'm not partial either way, just keeping it the same as when I bought it.. It really is running nice! Most likely would run the same or better with a Holley? I am going to install an Edelbrock intake (2101), to replace my cast intake though.

[jbwolfe]

Originally Posted by geezer#99

Looking forward to your new thread Haakon about 'I just bought this rebuilt carb and can't get it to run'!!
Just sayin'!!!

My thoughts exactly, considering that the carb I'm hassling with was "rebuilt" by "professionals".

Originally Posted by FLEET72

Was thinking the same thing....You are in my old stompin' grounds, I lived on what is now Ronald Reagan Blvd. OK, back to the topic.

jbwolfe, did you get it sorted out?

I haven't had the time to mess with it, but I did start reading the book about Q-Jets, and have already learned some really cool stuff. I have a another Q-Jet I bought from a friend that needs rebuilt, but is a complete unit that ran fine years ago. With the help of the book, I discovered that it is one of the better Q-Jets, nothing amazing, but a good solid carb to rebuild. I'm going to rebuild this one instead of messing with the "rebuilt" one.

I'm going to make this carb rebuild a winter project, have to finish up a few other projects around here, and clean up my shop so I have enough bench space to take it apart and keep track of everything.

Originally Posted by Haakon

I'm not partial either way, just keeping it the same as when I bought it.. It really is running nice! Most likely would run the same or better with a Holley? I am going to install an Edelbrock intake (2101), to replace my cast intake though.

Looks good! Glad your rebuilt carb worked out better than mine did

I'm learning that if I want something done right, I better just do it myself. It should be cheaper, it will eventually get done right, and I'll gain some more knowledge and maybe some new tools along the way.

[geezer#99]

Congrats Haakon!!
It's not always that way, what with the way they handle stuff during shipping.
Remember!
Keep the shiny side up and the greasy side down!!

[Haakon]

Originally Posted by geezer#99

Congrats Haakon!!
It's not always that way, what with the way they handle stuff during shipping.
Remember!
Keep the shiny side up and the greasy side down!!

Will do Boss!!